1. Field of the Invention
The present invention relates to an ink jet print head, and more particularly to a shear mode type ink jet print head.
2. Description of the Related Art
Recently, drop-on-demand type ink jet print heads have been greatly developed. The drop-on-demand type print head ejects only the ink droplets to be used for printing.
Representative examples of the drop-or-demand print heads include a Kyser type disclosed in U.S. Pat. No.4,339,763 and a thermal jet type disclosed in U.S. Pat. No. 5,159,349. Each type of these print heads, however, involves problems. The Kyser type is difficult to be modified into a smaller size. In the thermal jet type, inks are required to have high thermal resistance properties.
A shear mode type of ink jet print head has therefore been proposed to solve both of these problems. This shear mode type print head is disclosed in U.S. Pat. Nos. 4,879,568, 4,887,100, and 5,016,028 and in Japanese Patent Application Publication Kokai No. 5-92561.
A shear mode type print head is conceivable as shown in FIGS. 1 to 6. Directional terms such as "upper" "lower,""front," and "rear" used in the following explanations refer to the ink jet print head when in the posture shown in FIG. 3.
As shown in FIG. 3, the ink jet print head 1 is constructed from an actuator plate 2, a cover plate 3, a nozzle plate 31, and a driving substrate 41. The actuator plate 2 is formed from a piezoelectric material, such as a lead zirconium titanate (PZT) ceramic material, having ferroelectric properties. As shown in FIG. 1, the actuator plate 2 is polarized in an upward direction indicated by an arrow 5, and has a plurality of grooves 15 and side walls 11 separating the grooves 15. The cover plate 3 is formed from a ceramic material or a resin material. The actuator plate 2 and the cover plate 3 are bonded together by an adhesive layer 4 made from, for example, an epoxy adhesive. This forms the grooves 15 into a plurality of ink chambers 12. Thus formed ink chambers 12 are arranged with a certain interval in a horizontal direction A normal to the polarizing direction 5.
As apparent from FIG. 3, each of the ink chambers 12 extends along another horizontal direction 3 which is perpendicular to both the directions A and 5. Thus, each ink chamber 12 has an elongated shape. Each ink chamber 12 has perpendicular cross-section as shown in FIG. 1. The side walls 11 extend over the entire length of the ink chambers 12. A pair of electrodes 13 for applying a driving voltage through the side walls 11 are formed on both side surfaces of the side walls 11 from the top of the side walls 11 near the adhesive layer 4 to the middle of the side walls 11. Ink 81 is introduced to the ink chambers 12 from an ink supply port 21 via a manifold 22.
With the above-described structure, the ink jet print head 1 operates as described below. As shown in FIG. 2, when an ink chamber 12b, for example, is selected to eject an ink droplet according to desired print data, a positive driving voltage is applied to the electrodes 13c and 13d while the electrodes 13b and 13e are grounded. As a result, an electric field is generated in a direction 14a through the side wall 11a, and an electric field is generated in a direction 14b in the side wall 11b. The directions 14a and 14b of the electric fields are substantially normal to the polarization direction 5. This makes the side walls 11a and 11b deform inwardly due to a piezoelectric thickness shear effect. The deformation of the side walls 11a and 11b reduces the volume in the ink chamber 12b, thereby increasing the pressure of the ink 81 in the ink chamber 12b. This generates a pressure wave, whereby a portion of the ink 81 is ejected in the form of an ink droplet from a nozzle 32 connected with the ink chamber 12b.
When the application of the driving voltage is stopped, the side walls 11a and 11b return to their original positions shown in FIG. 1. This reduces the pressure of the ink 81 in the ink chamber 12b, whereby an additional ink 81 is supplied into the ink chamber 12b from the ink supply port 21 via the manifold 22.
In the above description, the driving voltage is applied in a direction so that the volume of the ink chamber 12b decreases, whereby an ink droplet is ejected from the ink chamber 12b. Alternatively, the driving voltage may be applied in an opposite direction so that the volume of the ink chamber 12b first increases and so that ink is additionally supplied to the ink chamber 12b. When the application of the driving voltage is stopped, the side walls 11a and 11b return to their original positions shown in FIG. 1, thereby ejecting an ink droplet.
According to the above-described driving operations, two adjacent ink chambers cannot be driven to eject ink droplets simultaneously. Accordingly, the plurality of ink chambers 12 in the actuator 2 are divided into at least two groups, and the two groups are driven alternately. For example, the ink chambers 12 are divided into two groups so that ink chambers 12b and 12d are in one group while an ink chamber 12c is in the other group. The two groups are alternately driven.
Next, the method of manufacturing the print head 1 will be described with reference to FIG. 3.
An actuator plate 2 which has been polarized in the direction 5 is first subjected to a grinding process using a thin disk-shaped diamond blade. This grinding process produces the parallel grooves 15 each being sandwiched between two adjacent side walls 11. The grooves 15 extend from a front end surface 16 in a direction toward the rear end surface 17. The grooves 15 have the same depth over nearly the whole actuator plate 2. However, at a certain position near to the rear end surface 17, the grooves 15 are made to gradually become shallower as they approach the rear end surface 17, thus forming parallel shallow grooves 18 near the rear end surface 17.
Electrodes 13 and 19 are then formed on the inner surfaces of both the grooves 15 and the shallow grooves 18 through a process such as a vacuum vapor deposition and a sputtering. This process is designed so that the floor and the lower half of the inner side surface of the grooves 15 will not be formed with the electrodes 13. For example, when a vacuum vapor deposition process is employed, the actuator plate 2 is tilted at an angle in relation to a direction in which metal vapor travels from a deposition source. The tilt angle is selected so that the floor and the lower half of the inner side surfaces of the grooves 15 are in a shadow with respect to the metal vapor travelling direction.
Then, electrodes are removed from the top surface portions of the side walls 11 through a process such as lapping. As a result, electrodes on both sides of the side walls 11 are separated from each other. Electrodes 13 thus remain only on the upper half of the inner side surfaces on the grooves 15. Electrodes 19 remain on the entire inner side surfaces and bottom surface of the shallow grooves 18. Each electrode 19 is for electrically connecting electrodes 13 formed on both inner side surfaces of a corresponding groove 15.
Then, a cover plate 3 made from a ceramic material or a resin material is subjected to a grinding or cutting process so that the ink supply port 21 and the manifold 22 are formed in the cover plate 3.
Next, the side of the actuator plate 2 with the grooves 15 formed and the side of the cover plate 3 with the manifold 22 formed are bonded at the surfaces by an adhesive layer 4 made from an epoxy adhesive or the like. As a result, each of the grooves 15 forms an ink chamber 12 with a shape as shown in FIG. 1. Then, a nozzle plate 31 formed with nozzles 32 in positions corresponding to the position of each of the ink chambers 12 is bonded to the front end surface 16 of the actuator plate 2 and to a front end of the cover plate 3.
Then, the driving substrate 41 is bonded to the side opposite the grooved side of the actuator plate 2 by an epoxy adhesive or the like. The substrate 41 is provided with conductor layer patterns 42 in positions corresponding to the position of each shallow groove 18. The electrode 19 on the bottom surface of the shallow groove 18 and the corresponding conductor layer pattern 42 are then connected by a conductor wire 43 through a wire-bonding process. Because the diameter of the conductor wire 43 is extremely small with little mechanical strength, an epoxy resin or the like is used for forming (potting) a protective film (not shown) to prevent contact and breaking of adjacent conductor wires 43 and corrosion due to moisture or dust particles in the air. The protective film is thermally set.
The above-described ink jet print head 1 is provided with a driving control unit. The driving control unit is constructed from a LSI chip 51 as shown in FIG. 4. Each of the conductor layer patterns 42 formed on the driving substrate 41 are individually connected to the LSI chip 51. A clock line 52, a data line 53, a voltage line 54, and a ground line 55 are also connected to the LSI chip 51. The LSI chip 51 determines which nozzle 32 to eject the ink droplet from according to data appearing in the data line 53 based on clock pulses successively supplied from the clock line 52. The LSI chip 51 applies a voltage V of the voltage line 54 to the conductor layer pattern 42 electrically connected to the electrode 3 in the ink chamber 12 that is determined to eject the ink. Also, the LSI chip 51 applies the zero voltage of the ground line 55 to the conductor layer patterns 42 electrically connected to the electrodes 13 in the other ink chambers 12 which are not to eject the ink.
The above-described print head 1 is mounted in a printer as shown in FIG. 5.
The ink jet print head 1 is mounted on a carriage 62. An ink supply tube 63 is connected to the ink supply port 21 of the print head 1. The LSI chip 51 is incorporated in the carriage 62. A flexible cable 64 protrudes from the carriage 62 and is connected to a control center (not shown). The flexible cable 64 encloses the clock line 52, the data line 53, the voltage line 54, and the ground line 55. The carriage 62 is capable of moving along a slider 66 over an entire width of a recording paper 71 in both directions 65. When the carriage 62 is moving, the ink jet print head 1 ejects ink droplets from the nozzles 32. This deposits ink droplets on the recording paper 71 supported on a platen roller 72.
More specifically, the recording paper 71 is stationary when the ink droplets are ejected from the ink jet print head 1. However, each time the carriage 62 performs a predetermined moving operation, the recording paper 71 is moved a fixed amount in a direction 75 by a pair of paper feed rollers 73 and 74. As a result, the ink jet print head 1 is able to form a desired character or image over the entire surface of the recording paper 71.
In the above-described ink jet print head 1, as shown in FIG. 1, only the upper half of each side wall 11 is provided with the electrode 13. The top surface of each side wall 11 is fixedly bonded to the cover plate 3. With this structure, only the upper half of the side wall 11 is applied with the driving voltage, and is deformed due to the piezoelectric thickness shear effect. The lower half is deformed following the upper half. Accordingly, the side wall 11 is bent at its middle portion as shown in FIG. 2.
According to this deformation mechanism, the side wall 11 can not be deformed with a large amount. The side wall 11 is deformed with a relatively small amount in comparison with the amount of the electric energy applied to the electrode 13. It is impossible to obtain a large volume reduction of the ink chamber 12. For this reason, a high driving voltage has to be applied to the electrode 13 in order that the ink chamber 12 will eject in droplets that have a velocity and a volume sufficient to from high quality images on the paper 71 located opposite the ink jet print head 1. Accordingly, a relatively complicated and large sized driving circuit has to be connected to the voltage line 54. This will limit lowering the cost and miniaturizing the printer.
In order to solve this problem, the print head 1 can be modified into a two actuator plate type print head 101 as shown in FIG. 6.
This print head 101 is constructed from two actuator plates 102 and 103, which are substantially identical to the actuator 2. The actuator plate 102 is formed with grooves 115 and side walls 111 separating the grooves 115. The actuator plate 102 is polarized in a direction 105. The actuator plate 103 is formed with other grooves 117 and side walls 116 separating the grooves 117. The actuator plate 103 is polarized in a direction 106. The top surfaces of the actuator plates 102 and 103 are bonded to each other so that an end of each side wall 111 is connected to an end of a corresponding side wall 116. As a result, the polarizing directions 105 and 106 of the plates 102 and 103 become opposite with each other. Thus connected side walls 111 and 116 form a single side wall 118. The side wall 118 has substantially twice as high as the side wall 11 of the print head 1. Each groove 115 and a corresponding groove 117 communicates with each other to form a single ink chamber 112. The volume of the ink chamber 112 is substantially twice as large as that of the ink chamber 12 of the print head 1.
According to this two plate type print head 101, both sides of each side wall 111 are entirely covered with electrodes 114. Similarly, both sides of each side wall 116 are entirely covered with electrodes 113. The connected portion of the side walls 111 and 116 is freely movable. Accordingly, when driving voltages are a plied to the electrodes 113 and 114, the side walls 11 and 116 are entirely deformed due to the piezoelectric thickness shear effect so that they are bent at their connected portion. Accordingly, the side walls can be bent with an amount substantially twice as large as the amount, with which the side walls of FIG. 2 are bent, even when the same driving voltages are applied. The print head 101 can therefore generate the same ink pressure as does the ink jet print head 1 even when applied with only a half the driving voltage applied to the ink jet print head 1. The print head 101 can thus be driven with a driving voltage less than that applied to the ink jet print head 1. Accordingly, the print head 101 can be employed with a simpler driving circuit and therefore can be produced with a lower production cost. Additionally, the actuator plates 102 and 103 can be more reliably driven. The piezoelectric ceramic constituting the actuator plates have to be driven with a driving voltage lower than a predetermined amount of limit voltage. If a voltage higher than the limit voltage is applied to the actuator plates, the polarization formed in the piezoelectric ceramic will be broken down. According to this two actuator type print head, however, the actuator plates can be driven with a voltage sufficiently lower than the limit voltage. Accordingly, it is possible to drive the actuator plate with higher reliability.
It is, however, very difficult to actually produce two actuator plates 102 and 103 having exactly the same sizes. It is also very difficult to bond the two actuator plates 102 and 103 so that the side walls 111 and 116 be positioned accurately in correspondence with each other with no shifts.